LOCALIZED H-1-MR SPECTROSCOPY FOR METABOLIC CHARACTERIZATION OF DIFFUSE AND FOCAL BRAIN-LESIONS IN PATIENTS INFECTED WITH HIV

Objectives-To evaluate the role of proton MR spectroscopy (H-1-MRS) in detecting metabolic changes in diffuse or focal lesions in the brain of patients infected with HIV. Methods-Sixty HIV seropositive patients (25 with HIV related encephalopathies, 20 with toxoplasmosis, eight w ith progressive multifocal leukoencephalopathies (PMLs), and seven wit h lymphomas) and 22 HIV seronegative neurological controls were examin ed with a combined MRI and H-1-MRS technique using a Siemens 1.5 Tesla Magnetom. Spectra (Spin Echo sequence, TE 135 ms) were acquired by si ngle voxel, localised on focal lesions in toxoplasmosis, PML, lymphoma s, and HIV encephalopathies and on the centrum semiovale of neurologic al controls. Choline (Cho), creatine (Cr), N-acetyl aspartate (NAA), l actate, and lipids were evaluated in each spectrum and NAA/Cr, NAA/Cho , and Cho/Cr ratios were calculated. Results-A significant decrease in NAA/Cr and NAA/Cho ratios were found in all Mn: diagnostic groups in comparison with neurological controls (p<0.003), suggesting neuronal o r axonal damage independent of brain lesion aetiology. However, the NA A/Cr ratio was significantly lower in PML and lymphomas than in HIV en cephalopathies (p<0.02) and toxoplasmosis (p<0.05). HIV encephalopathi es, lymphomas, and toxoplasmosis showed a significant increase in the Cho/Cr ratio in comparison with neurological controls (p<0.03) without between group differences. The presence of a lipid signal was more fr equent in lymphomas (71%) than in other HIV groups (Fisher's test, p=0 .00003). The presence of mobile lipid resonance together with a high C ho/Cr ratio in lymphomas may be related to an increased membrane synth esis and turnover in tumour cells. A lactate signal (marker of inflamm atory reaction), was found in all but one patient with PML lesions (75 %),but had a lower incidence in the other MV diagnostic groups (Fisher 's test, p=0.00024). Conclusion-H-1-MRS shows a high sensitivity in de tecting brain involvement in HIV related diseases, but a poor specific ity in differential diagnosis of HIV brain lesions. Nevertheless,the h omogeneous metabolic pattern that characterises PML suggests the usefu lness of H-1-MRS as an adjunct to MRI in differentiating CNS white mat ter lesions, such as HIV encephalopathies, from PML.